1. Field of the Invention
The invention relates to a rotary-anode X-ray tube whose anode is connected to a bearing portion which is rotatable about an axis of rotation and which cooperates with a stationary bearing portion in which there is provided a cavity which extends in the direction of the axis of rotation and the side walls of which can be cooled by means of a cooling medium circuit.
2. Description of the Related Art
A rotary-anode X-ray tube of this kind is known from EP-OS 430 367which corresponds to U.S. Pat. No. 5,091,927. The known rotary-anode X-ray tube comprises a sleeve bearing in the form of a so-called helical groove bearing in which a liquid lubricant, for example a gallium alloy, is present between the rotatable bearing portion and the stationary bearing portion. Via this lubricant, a substantial flow of heat can be transferred from the rotatable bearing portion to the stationary bearing portion, notably to the side walls thereof. Therefore, effective cooling of the stationary bearing portion is required; to this end, it comprises a cylindrical cavity which has a circular cross-section and which extends in the direction of the axis of rotation. In the known rotary-anode X-ray tube, said cavity accommodates a cooling medium guide device which directs the cooling medium, arriving via a tube within the guide device, to the space between the tube and the side walls so that the cooling medium flows several times around the tube. This results in effective cooling, but the cooling medium guide device causes a substantial pressure drop so that the pump producing the circulation of the cooling medium in the cooling medium circuit must be designed for a high feed pressure.